Drive unit for variable displacement electric compressor

ABSTRACT

A compressor is actuated by a motor and varies the displacement by the operation of an electromagnetic actuator. A drive unit of the compressor includes a power source, a motor drive circuit located on a power supply path between the motor and the power source, and an actuator drive circuit located on a power supply path between an electromagnetic actuator and the power source. The motor drive circuit drives the motor and the actuator drive circuit drives the electromagnetic actuator. The motor drive circuit and the actuator drive circuit share a smoothing circuit and a filter circuit. Therefore, the actuator drive circuit does not require its own smoothing circuit and a filter circuit. This reduces the number of parts of the drive unit, thereby reducing the size and the cost of the drive unit.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a drive unit for a variable displacement electric compressor, which can vary the displacement using an electromagnetic actuator. More specifically, the present invention pertains to a drive unit for driving a motor and an electromagnetic actuator based on a command signal sent from a command device.

[0002] A typical drive unit includes a system for controlling a variable displacement electric compressor (hereinafter, simply referred to as a compressor) used for a vehicular air-conditioner. The system includes, for example, an electronic control unit (ECU), a motor drive circuit (such as an inverter), and a valve drive circuit (such as PWM circuit) for driving an electromagnetic valve. The ECU is a computer that controls the air-conditioner. The motor drive circuit is arranged on a power supply path between a vehicular battery and the motor. The valve drive circuit is arranged on a power supply path between the vehicular battery and the electromagnetic valve.

[0003] The ECU determines that the compressor needs to be activated or stopped in accordance with whether there is a need for air-conditioning and then commands the motor drive circuit. The motor drive circuit supplies or stops supplying power to the motor in accordance with the command sent from the ECU. Accordingly, the compressor is activated or stopped. The ECU determines the duty ratio in accordance with the information such as the in-car temperature and a target temperature. The ECU then commands the valve drive circuit to drive the electromagnetic valve with the determined duty ratio. The valve drive circuit drives the electromagnetic valve with the duty ratio commanded by the ECU to control the opening degree of the electromagnetic valve, or the displacement of the compressor.

[0004] However, the motor drive circuit and the valve drive circuit are separate circuits. Therefore, electric elements forming each circuit are exclusively used. That is, an electric element forming a filter circuit to filter noise from the power source and an electric element forming a smoothing circuit for stabilizing direct-current voltage applied to each circuit are exclusively provided for each drive circuit. This increases the size and the cost of the control system for compressor.

SUMMARY OF THE INVENTION

[0005] Accordingly, it is an objective of the present invention to provide a drive unit for a variable displacement electric compressor in which electric elements are shared between a motor drive circuit and an actuator drive circuit for driving an electromagnetic actuator.

[0006] To achieve the above objective, the present invention provides a drive unit of a compressor that is actuated by a motor to compress gas and varies the displacement by the operation of an electromagnetic actuator. The drive unit includes a power source, a motor drive circuit, and an actuator drive circuit. The motor drive circuit is located on a power supply path between the motor and the power source. The motor drive circuit drives the motor in accordance with an external command signal. The actuator drive circuit is located on a power supply path between the electromagnetic actuator and the power source. The actuator drive circuit drives the electromagnetic actuator in accordance with an external command signal. One of the drive circuits includes an electric element, which electrically affects the other drive circuit.

[0007] Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] The invention, together with objects and advantages thereof, may best be understood by reference to the following description of the presently preferred embodiments together with the accompanying drawings in which:

[0009]FIG. 1 is a cross-sectional view illustrating a swash plate type variable displacement electric compressor according to a first embodiment of the present invention;

[0010]FIG. 2 is a cross-sectional view illustrating the control valve located in the compressor shown in FIG. 1;

[0011]FIG. 3 is a block circuit diagram illustrating a system for controlling the compressor shown in FIG. 1:

[0012]FIG. 4 is a block circuit diagram illustrating a control system according to a second embodiment of the present invention: and

[0013]FIG. 5 is a block circuit diagram illustrating a control system according to a third embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] A first embodiment of the present invention will now be described with reference to FIGS. 1 to 3.

[0015] As shown in FIG. 1, a swash plate type variable displacement electric compressor (hereinafter, simply referred to as a compressor) has a housing assembly 11. The housing assembly 11 defines a control chamber, which is a crank chamber 12 in the first embodiment. A drive shaft 13 is rotatably supported by the housing assembly 11 and extends through the crank chamber 12. The drive shaft 13 is coupled to a drive source, which is an engine E in the first embodiment, by a power transmission mechanism PT. The engine E may be, and not limited to, an internal combustion engine including a gasoline engine.

[0016] The power transmission mechanism PT includes a pulley 80, which is rotatably supported by the housing assembly 11, and a belt 81, which couples the pulley 80 to the engine E. A hub 82 is secured to the end portion of the drive shaft 13 that projects outside the housing assembly 11. A conventional one-way clutch 83 is arranged between the pulley 80 and the hub 82.

[0017] An AC motor 84 is arranged inside the hub 82. The motor 84 includes a stator 84 a, which is secured to the housing assembly 11, and a rotor 84 b, which is secured to the hub 82 to surround the outer circumference of the stator 84 a. For example, when the engine E is stopped, the motor 84 generates a rotational force on the rotor 84 b by the electromagnetic induction generated by the power supply to the stator 84 a. This rotates the drive shaft 13 via the hub 82.

[0018] At this time, the one-way clutch 83 prevents power from being transmitted from the hub 82 to the pulley 80. Therefore, the rotational force generated by the motor 84 is prevented from being transmitted to the engine E. The one-way clutch 83 permits power transmission from the pulley 80 to the hub 82. Therefore, the power of the engine E is transmitted to the drive shaft 13 via the pulley 80 and the hub 82.

[0019] A lug plate 14 is fixed to the drive shaft 13 in the crank chamber 12 to rotate integrally with the drive shaft 13. A swash plate 15 is accommodated in the crank chamber 12. The swash plate 15 slides along and inclines with respect to the drive shaft 13.

[0020] A hinge mechanism 16 is arranged between the lug plate 14 and the swash plate 15. Therefore, the swash plate 15 rotates integrally with the lug plate 14 and the drive shaft 13 and inclines with respect to the drive shaft 13.

[0021] The housing assembly 11 has cylinder bores 11 a (only one is shown). Each cylinder bore 11 a accommodates a single-headed piston 17. Each piston 17 reciprocates inside the corresponding cylinder bore 11 a. Each piston 17 is coupled to the peripheral portion of the swash plate 15 by a pair of shoes 18. Accordingly, the shoes 18 convert the rotation of the swash plate 15, which rotates with the drive shaft 13, to reciprocation of the pistons 17.

[0022] The housing assembly 11 includes a valve plate assembly 19, which closes the openings of the cylinder bores 11 a on one end. The valve plate assembly 19 has suction ports 23, suction valve flaps 24, discharge ports 25 and discharge valve flaps 26. Each set of the suction port 23, the suction valve flap 24, the discharge port 25 and the discharge valve flap 26 corresponds to one of the cylinder bores 11 a. A compression chamber 20 is defined in each cylinder bore 11 a by the associated piston 17 and the valve plate assembly 19. The housing assembly 11 defines a suction chamber 21 and a discharge chamber 22 opposite to the cylinder bores 11 a with the valve plate assembly 19 arranged in between.

[0023] As each piston 17 moves from the top dead center to the bottom dead center, refrigerant gas in the suction chamber 21 is drawn into the corresponding compression chamber 20 through the corresponding suction port 23 while flexing the suction valve flap 24 to an open position. Refrigerant gas that is drawn into the compression chamber 20 is compressed to a predetermined pressure as the piston 17 is moved from the bottom dead center to the top dead center. Then, the gas is discharged to the discharge chamber 22 through the corresponding discharge port 25 while flexing the discharge valve flap 26 to an open position.

[0024] As shown in FIG. 1, a bleed passage 27 and a supply passage 28 are formed in the housing assembly 11. The bleed passage 27 connects the crank chamber 12 with the suction chamber 21. The supply passage 28 connects the crank chamber 12 with the discharge chamber 22. The supply passage 28 is regulated by the control valve CV.

[0025] The opening of the control valve CV is adjusted to control the balance of the flow rate of highly pressurized gas supplied to the crank chamber 12 through the supply passage 28 and the flow rate of gas conducted out from the crank chamber 12 through the bleed passage 27. The pressure in the crank chamber 12 is thus adjusted. As the pressure in the crank chamber 12 varies, the inclination angle of the swash plate 15 is changed. Accordingly, the stroke of each piston 17, or the compressor displacement, is varied.

[0026] For example, a decrease in the pressure in the crank chamber 12 increases the inclination angle of the swash plate 15, which increases the displacement of the compressor. On the contrary, an increase in the pressure in the crank chamber 12 decreases the inclination angle of the swash plate 15, which decreases the displacement of the compressor.

[0027] As shown in FIG. 1, the refrigerant circuit of the vehicular air-conditioner includes the compressor and an external refrigerant circuit 30, which is connected to the compressor. The external refrigerant circuit 30 includes a condenser 31, an expansion valve 32, and an evaporator 33.

[0028] A first pressure monitoring point PI is located inside the discharge chamber 22. A second pressure monitoring point P2 is located in the refrigerant passage at a part that is spaced away from the first pressure monitoring point P1 toward the condenser 31 by a predetermined distance. The first pressure monitoring point PI is connected to the control valve CV through a first pressure introduction passage 35. As shown in FIG. 2, the second pressure monitoring point P2 is connected to the control valve CV through a second pressure introduction passage 36.

[0029] As shown in FIG. 2, the control valve CV has a valve housing 41. A valve chamber 42, a communication passage 43, and a pressure sensing chamber 44 are defined in the valve housing 41. A transmission rod 45 extends through the valve chamber 42 and the communication passage 43. The transmission rod 45 moves in the axial direction, or in the vertical direction as viewed in FIG. 2.

[0030] The communication passage 43 is disconnected from the pressure sensing chamber 44 by the upper portion of the transmission rod 45, which is fitted in the communication passage 43. The valve chamber 42 is connected to the discharge chamber 22 through an upstream section of the supply passage 28. The communication passage 43 is connected to the crank chamber 12 through a downstream section of the supply passage 28. The valve chamber 42 and the communication passage 43 form a part of the supply passage 28.

[0031] A valve body 46 is formed in the middle portion of the transmission rod 45 and is located in the valve chamber 42. A step defined between the valve chamber 42 and the communication passage 43 functions as a valve seat 47. The communication passage 43 serves as a valve hole. The transmission rod 45 shown in FIG. 2 is located at the lowermost position where the opening degree of the valve hole 43 is the greatest. When the transmission rod 45 is moved from the lowermost position to the uppermost position, at which the valve body 46 contacts the valve seat 47, the communication passage 43 is disconnected from the valve chamber 42. The opening degree of the valve hole 43, or the opening degree of the supply passage 28, is controlled in accordance with the axial position of the transmission rod 45.

[0032] A pressure sensing member, which is a bellows 48 in the first embodiment, is located in the pressure sensing chamber 44. The upper end of the bellows 48 is fixed to the valve housing 41. The lower end of the bellows 48 receives the upper end of the transmission rod 45. The bellows 48 divides the pressure sensing chamber 44 into a first pressure chamber 49, which is the interior of the bellows 48, and a second pressure chamber 50, which is the exterior of the bellows 48. The first pressure chamber 49 is connected to the first pressure monitoring point P1 through a first pressure introduction passage 35. The second pressure chamber 50 is connected to the second pressure monitoring point P2 through a second pressure introduction passage 36. Therefore, the first pressure chamber 49 is exposed to the pressure PdH monitored at the first pressure monitoring point P1, and the second pressure chamber 50 is exposed to the pressure PdL monitored at the second pressure monitoring point P2.

[0033] An electromagnetic actuator 51 is coupled to the lower portion of the valve housing 41. The electromagnetic actuator 51 includes a cup-shaped cylinder 52, which is arranged coaxial to the valve housing 41. A stationary iron core 53 is fitted in the upper opening of the cylinder 52 and is secured to the cylinder 52. The stationary core 53 defines a plunger chamber 54 at the lowermost portion in the cylinder 52.

[0034] A movable iron core 56 is located in the plunger chamber 54. The movable iron core 56 slides along the plunger chamber 54 in the axial direction. An axial guide hole 57 is formed in the center of the stationary iron core 53. The transmission rod 45 is inserted in the guide hole 57. The lower end of the transmission rod 45 contacts the top surface of the movable iron core 56 inside the plunger chamber 54.

[0035] The plunger chamber 54 accommodates a spring 60. The spring 60 urges the plunger 56 toward the transmission rod 45. The transmission rod 45 is urged toward the movable iron core 56 by the force of the bellows 48. Therefore, the plunger 56 always moves up and down integrally with the transmission rod 45.

[0036] A coil 61 is located about the stationary iron core 53 and the movable iron core 56. The coil 61 generates an electromagnetic force (electromagnetic attracting force), the magnitude of which depends on the value of the supplied current, between the movable iron core 56 and the stationary iron core 53. The electromagnetic force is transmitted to the transmission rod 45 via the movable iron core 56.

[0037] The position of the transmission rod 45 (the valve body 46), or the valve opening of the control valve CV, is controlled in the following manner.

[0038] As shown in FIG. 2, when the coil 61 is supplied with no electric current (duty ratio=0%), the position of the transmission rod 45 is dominantly determined by the downward force of the bellows 48. Thus, the transmission rod 45 is placed at its lowermost position, and the communication passage 43 is fully opened. The difference between the pressure in the crank chamber 12 and the pressure in the compression chambers 20 thus becomes great. As a result, the inclination angle of the swash plate 15 is minimized, and the discharge displacement of the compressor is also minimized.

[0039] When a current of the minimum duty ratio, which is greater than 0%, is supplied to the coil 61 of the control valve CV, the upward electromagnetic force surpasses the downward forces of the bellows 48, which moves the transmission rod 45 upward. In this state, the resultant of the upward electromagnetic force and upward force of the spring 60 act against the resultant of the force based on the pressure difference ΔPd (Pd=PdH−PdL) and the downward forces of the bellows 48. The position of the valve body 46 of the transmission rod 45 relative to the valve seat 47 is determined such that upward and downward forces are balanced.

[0040] For example, if the flow rate of the refrigerant in the refrigerant circuit is decreased due to a decrease in speed of the engine E, the downward force based on the pressure difference ΔPd decreases, and the electromagnetic force cannot balance the forces acting on the transmission rod 45. Therefore, the transmission rod 45 (the valve body 46) moves upward. This decreases the opening degree of the communication passage 43 and thus lowers the pressure in the crank chamber 12. Accordingly, the inclination angle of the swash plate 15 is increased, and the displacement of the compressor is increased. The increase in the displacement of the compressor increases the flow rate of the refrigerant in the refrigerant circuit, which increases the pressure difference ΔPd.

[0041] In contrast, when the flow rate of the refrigerant in the refrigerant circuit is increased due to an increase in the speed of the engine E, the downward force based on the pressure difference ΔPd increases and the current electromagnetic force cannot balance the forces acting on the transmission rod 45. Therefore, the transmission rod 45 (the valve body 46) moves downward and increases the opening degree of the communication passage 43. This increases the pressure in the crank chamber 12. Accordingly, the inclination angle of the swash plate 15 is decreased, and the displacement of the compressor is also decreased. The decrease in the displacement of the compressor decreases the flow rate of the refrigerant in the refrigerant circuit, which decreases the pressure difference ΔPd.

[0042] When the duty ratio of the electric current supplied to the coil 61 is increased to increase the electromagnetic force, the pressure difference ΔPd cannot balance the forces acting on the transmission rod 45. Therefore, the transmission rod 45 (the valve body 46) moves upward and decreases the opening degree of the communication passage 43. As a result, the displacement of the compressor is increased. Accordingly, the flow rate of the refrigerant in the refrigerant circuit is increased and the pressure difference ΔPd is increased.

[0043] When the duty ratio of the electric current supplied to the coil 61 is decreased and the electromagnetic force is decreased accordingly, the pressure difference ΔPd cannot balance the forces acting on the transmission rod 45. Therefore, the transmission rod 45 (the valve body 46) moves downward, which increases the opening degree of the communication passage 43. Accordingly, the compressor displacement is decreased. As a result, the flow rate of the refrigerant in the refrigerant circuit is decreased, and the pressure difference ΔPd is decreased.

[0044] As described above, the target value of the pressure difference ΔPd (target pressure difference) is determined by the duty ratio of current supplied to the coil 61. The control valve CV automatically determines the position of the transmission rod 45 (the valve body 46) according to changes of the pressure difference ΔPd to maintain the target pressure difference ΔPd. The target pressure difference ΔPd is externally controlled by adjusting the duty ratio of current supplied to the coil 61.

[0045] As shown in FIG. 3, a system for controlling the compressor includes a controller, which is an electronic control unit (ECU) 65 in the first embodiment, a detection apparatus 79, and a drive unit 66. The ECU 65 is a computer that has a CPU, a ROM, a RAM, and an I/O.

[0046] The drive unit 66 includes a controller 67, a motor drive circuit, which is an inverter circuit 68 in the first embodiment, and an actuator drive circuit for driving an electromagnetic actuator, which is a pulse width modulation (PWM) circuit 69 in the first embodiment. The controller 67 is connected to the ECU 65 via, for example, a LAN in a vehicle. The inverter circuit 68 is arranged on a power supply path between a direct-current power source, which is a battery Bt in the first embodiment, and a stator 84 a of the motor 84. The PWM circuit 69 is arranged on a power supply passage between the battery Bt and a coil 61 of the control valve CV. The inverter circuit 68 and the PWM circuit 69 are located on the same substrate. The inverter circuit 68, the PWM circuit 69, and the controller 67 are accommodated in the case (not shown) and form a single circuit unit.

[0047] The inverter circuit 68 includes phase inverter circuits 68 a (three phase inverter circuits 68 a are arranged in the first embodiment). Each phase inverter circuit 68 a includes a high-side switching element (an IGBT is used in the first embodiment) 70 and a low-side switching element (an IGBT is used in the first embodiment) 71. Each high-side switching element 70 includes a control terminal (gate terminal), which is connected to the controller 67, and first and second terminals. Similarly, each low-side switching element 71 includes a control terminal (gate terminal), which is connected to the controller 67, and first and second terminals. The first terminal (collector terminal) of each high-side switching element 70 is connected to the high potential terminal of the battery Bt. The first terminal (emitter terminal) of the low-side switching element 71 is connected to the low potential terminal of the battery Bt. The second terminal (emitter terminal) of the high-side switching element 70 and the second terminal (collector terminal) of the low-side switching element 71 are connected to a common AC output terminal 68 b. The AC output terminal 68 b of each phase inverter circuit 68 a is connected to one of winding wires of the stator 84 a of the motor 84. A flywheel diode 72 is connected between the first terminal and the second terminal of each of the switching elements 70, 71.

[0048] The inverter circuit 68 includes a smoothing circuit (smoothing capacitor) 73 and a filter circuit 74. The smoothing circuit 73 stabilizes the voltage of the battery BT applied to the inverter circuit 68. The filter circuit 74 includes an LC circuit, which has a coil 74 a and a capacitor 74 b. The filter circuit 74 filters noise that enters the inverter circuit 68 from the battery Bt.

[0049] The PWM circuit 69 includes a switching element (an IGBT is used in the first embodiment) 75 and a flywheel diode 76. The switching element 75 includes a control terminal (gate terminal), which is connected to the controller 67, a first terminal (emitter terminal), which is connected to the high potential terminal of the battery Bt, and a second terminal (collector terminal), which is connected to a cathode of the flywheel diode 76. An anode of the flywheel diode 76 is connected to the low potential terminal of the battery Bt. The coil 61 of the control valve CV includes a first terminal, which is connected to the low potential terminal of the battery Bt via a shunt resistor 77, and a second terminal, which is connected to the second terminal of the switching element 75 and the cathode of the flywheel diode 76. The controller 67 detects the current value that flows through the coil 61 with the shunt resistor 77.

[0050] In the drive unit 66, the electric elements that form the inverter circuit 68 electrically affect the PWM circuit 69. That is, a battery voltage input terminal of the PWM circuit 69, or the first terminal of the switching element 75, is connected to a battery voltage output terminal (a connecting point SP shown in FIG. 3) of the inverter circuit 68. Therefore, the smoothing circuit 73 of the inverter circuit 68 also stabilizes the battery voltage applied to the PWM circuit 69. The filter circuit 74 of the inverter circuit 68 also filters noise from the battery Bt to the PWM circuit 69. Thus, the PWM circuit 69 does not have its own smoothing circuit and a filter circuit but shares the smoothing circuit 73 and the filter circuit 74 with the inverter circuit 68.

[0051] The ECU 65 determines the target pressure difference in accordance with the information (on-off state of the air conditioner, the in-car temperature, and a target temperature) from the detection apparatus 79 and sends the target pressure difference to the controller 67 of the drive unit 66. The controller 67 calculates the current value that corresponds to the target pressure difference received from the ECU 65. The controller 67 then controls the duty ratio to the switching element 75 of the PWM circuit 69 such that the current value from the shunt resistor 77 is equivalent to the calculated current value.

[0052] The ECU 65 drives an air-conditioning control actuator unit 86, which includes actuators other than the control valve CV. The actuator unit 86 includes, for example, a servo motor, which actuates the inside/outside air switching door, a blower motor, a servo motor for actuating an air-mix door. The control valve CV, or the displacement of the compressor is controlled regardless of whether the compressor is actuated by the engine E or the motor 84. That is, even when the compressor is actuated by the motor 84, the cooling performance of the air-conditioner is changed by controlling the displacement of the compressor and not by adjusting the rotational speed of the motor 84.

[0053] If it is determined that the compressor needs to be operated based on the information from the detection apparatus 79 when the engine E is stopped, the ECU 65 sends a command signal to the controller 67 of the drive unit 66 to operate the motor 84. At the receipt of the command signal, the controller 67 switches on the low-side switching elements 71 each phased by 120 degrees by intermittently controlling the switching elements 70, 71 of the inverter circuit 68. The controller 67 then forms a pseudo three-phase AC voltage by controlling the duty ratio to the high side switching elements 70 to apply the voltage to the motor 84. This rotates the motor 84 thereby activating the compressor. Thus, the air in the passenger compartment can be conditioned even when the engine E is stopped. The controller 67 commands the inverter circuit 68 to rotate the motor 84 approximately at a constant speed.

[0054] The present invention provides the following advantages.

[0055] The smoothing circuit 73 and the filter circuit 74, which form a part of the inverter circuit 68, operate also for the PWM circuit 69. Therefore, as mentioned above, instead of having its own smoothing circuit and a filter circuit, the PWM circuit 69 can share the electric elements, which form the smoothing circuit 73 and the filter circuit 74, with the inverter circuit 68. This reduces the number of parts required for the drive unit 66, which in turn reduces the size and the cost of the drive unit 66.

[0056] In the prior art, the smoothing circuit and the filter circuit withstand several hundred watts and the smoothing circuit and the filter circuit used in the valve drive circuit withstand several ten watts. Therefore, when the smoothing circuit 73 and the filter circuit 74 are shared between the inverter circuit 68 and the PWM circuit 69 as in the first embodiment of the present invention, it is not required to change the capacity of the smoothing circuit and the filter circuit, which are used in the prior art motor drive circuit. Therefore, the smoothing circuit and the filter circuit that are used in the prior art motor drive circuit can be used without change. Therefore, there is no increase in the cost due to modification of the capacity of the smoothing circuit and the filter circuit. That is, the present invention is particularly effective for an apparatus that has a motor drive circuit and a valve drive circuit for driving an electromagnetic valve.

[0057] The switching element 75 of the PWM circuit 69 has the first terminal, which is connected to the high potential terminal of the battery Bt, and the second terminal, which is connected to the second terminal of the coil 61 of the control valve CV. The first terminal of the coil 61 is connected to the low potential terminal of the battery Bt via the shunt resistor 77. Arranging the shunt resistor 77 between the first terminal of the coil 61 and the low potential terminal of the battery Bt allows detecting the value of the current flowing through the coil 61. That is, the value of the current flowing through the coil 61 can be detected using the shunt resistor 77, which is inexpensive. Thus, the cost of the drive unit 66 is further reduced.

[0058] A second embodiment of the present invention will now be described with reference to FIG. 4. The differences from the first embodiment shown in FIGS. 1 to 3 will mainly be discussed below.

[0059] As shown in FIG. 4, the PWM circuit 69 according to the second embodiment includes a first terminal (emitter terminal), which is connected to the low potential terminal of the battery Bt, and a second terminal (collector terminal), which is connected to the anode of the flywheel diode 76. The cathode of the flywheel diode 76 is connected to the high potential terminal of the battery Bt. The coil 61 of the control valve CV has a first terminal, which is connected to the high potential terminal of the battery Bt, and a second terminal, which is connected to the second terminal of the switching element 75 and the anode of the flywheel diode 76.

[0060] Therefore, the emitter potential of the switching element 75 of the PWM circuit 69 becomes equivalent to the ground level. The emitter potential of the low-side switching elements 71 of the inverter circuit 68 also becomes equivalent to the ground level. The controller 67 has a gate drive source 67 a, which is connected to the control terminal (gate terminal) of each of the switching element 75 and the low-side switching elements 71. That is, the switching element 75 of the PWM circuit 69 and the low-side switching elements 71 of the inverter circuit 68 are driven by the common gate drive source 67 a.

[0061] The controller 67 has gate drive sources 67 b each of which corresponds to one of the high-side switching elements 70 of the inverter circuit 68. The emitter potential of each high-side switching element 70 fluctuates in accordance with the on-off state of the corresponding low-side switching element 71 in the same phase inverter circuit 68 a. Therefore, it is difficult to share the gate drive source 67 a among all the high-side switching elements 70. Also, the shunt resistor 77 is eliminated in the second embodiment and a hall element, which is not shown, is used instead to detect the value of the current flowing through the coil 61.

[0062] In the second embodiment, the same advantages as the first embodiment shown in FIGS. 1 to 3 are provided. Particularly, in the second embodiment, the switching element 75 of the PWM circuit 69 and the low-side switching elements 71 of the inverter circuit 68 are connected to the common gate drive source 67 a. This simplifies the structure of the controller 67 and further reduces the cost of the drive unit 66.

[0063] A third embodiment of the present invention will now be described with reference to FIG. 5. The differences from the first embodiment shown in FIGS. 1 to 3 will mainly be discussed.

[0064] As shown in FIG. 5, in the third embodiment, a stepping motor (DC motor) is used for the motor 84 instead of the AC motor. A motor drive circuit 91 includes switching circuits 91 a, the number of which corresponds to the number of phases of the motor 84 (three switching circuits 91 a are arranged in the third embodiment). Each switching circuit 91 a includes a switching element (an IGBT is used in the third embodiment) 93 and a flywheel diode 92. Each switching element 93 includes a first terminal (collector terminal), which is connected to the low potential terminal of the battery Bt, and a second terminal (emitter terminal), which is connected to the anode of the corresponding flywheel diode 92. The cathode of each flywheel diode 92 is connected to the high potential terminal of the battery Bt. In each switching circuit 91 a, the second terminal of the switching element 93 and the anode of the flywheel diode 92 are connected to one of winding wires of the stator 84 a of the motor 84.

[0065] The structure of the PWM circuit 69 is the same as that of the second embodiment shown in FIG. 4. The first terminal of the coil 61 of the control valve CV is connected to the high potential terminal of the battery Bt via a power line 95. A common terminal (neutral point) of three winding wires of the stator 84 a is connected to the power line 95 via a power line 96. That is, the neutral point of the winding wires of the stator 84 a is connected to the high potential terminal of the battery Bt via the power lines 96, 95. Therefore, the motor 84 and the control valve CV are connected to the drive unit 66 via the common power line 95.

[0066] In the third embodiment, the same advantages as the first embodiment shown in FIGS. 1 to 3 are also provided. Particularly, in the third embodiment, the DC motor is used for the motor 84. Therefore, the structure of the motor drive circuit 91 and the controller 67 is simplified. Also, using the DC motor for the motor 84 allows the motor 84 and the control valve CV to be connected to the drive unit 66 via the common power line 95. This simplifies the wiring.

[0067] It should be apparent to those skilled in the art that the present invention may be embodied in many other specific forms without departing from the spirit or scope of the invention. Particularly, it should be understood that the invention may be embodied in the following forms.

[0068] The ECU 65 may serve as the controller 67 instead of the controller 67.

[0069] The switching elements 70, 71, 75, 93 may not be the IGBT. The switching elements 70, 71, 75, 93 may be switching elements such as power MOS-FET.

[0070] The first pressure monitoring point P1 may be located in the suction pressure zone (low pressure zone), and the second pressure monitoring point P2 may be located at a part downstream of the first pressure monitoring point P1 in the suction pressure zone. The low pressure zone includes the evaporator 33, the suction chamber 21, and the refrigerant passage between the evaporator 33 and the suction chamber 21.

[0071] The first pressure monitoring point P1 may be located in the discharge pressure zone (high pressure zone), and the second pressure monitoring point P2 may be located in the low pressure zone. The high pressure zone includes the discharge chamber 22, the condenser 31, and the refrigerant passage between the discharge chamber 22 and the condenser 31.

[0072] The first pressure monitoring point P1 may be located in the high pressure zone, and the second pressure monitoring point P2 may be located in the crank chamber 12. Alternately, the second pressure monitoring point P2 may be located in the crank chamber 12, and the first pressure monitoring point P1 may be located in the low pressure zone.

[0073] The pressure monitoring points P1, P2 may be located anywhere as long as the pressure monitoring points P1, P2 are located in the refrigerant circuit, that is, the high pressure zone, the low pressure zone, and a medium pressure zone, which is the crank chamber 12.

[0074] The control valve CV may be a variable target suction pressure type control valve, which changes the target suction pressure, or a variable target discharge pressure type control valve, which changes the target discharge pressure, instead of the variable target pressure difference type control valve, which changes the target pressure difference. The variable target suction (discharge) pressure type control valve CV includes a pressure sensing mechanism and a target pressure changing mechanism. The pressure sensing mechanism moves the valve body to change the displacement of the compressor such that the mechanically detected suction pressure (discharge pressure) converges to the target value. The target pressure changing mechanism changes the target suction pressure (target discharge pressure) by adjusting the force applied to the valve body by the external command.

[0075] The control valve may be an electromagnetic valve that does not have the pressure sensing mechanism.

[0076] The present invention may be applied to a drive unit of an electromagnetic actuator, which directly changes the inclination of the swash plate.

[0077] The present invention may be applied to a drive unit of a motor used in a compressor that is actuated only by a motor, such as a compressor used in an air-conditioner of an electric automobile and a compressor used in an air-conditioner for home use.

[0078] Therefore, the present examples and embodiments are to be considered as illustrative and not restrictive and the invention is not to be limited to the details given herein, but may be modified within the scope and equivalence of the appended claims. 

1. A drive unit of a compressor that is actuated by a motor to compress gas and varies the displacement by the operation of an electromagnetic actuator, the drive unit comprising: a power source; a motor drive circuit located on a power supply path between the motor and the power source, wherein the motor drive circuit drives the motor in accordance with an external command signal; and an actuator drive circuit located on a power supply path between the electromagnetic actuator and the power source, wherein the actuator drive circuit drives the electromagnetic actuator in accordance with an external command signal, and wherein one of the drive circuits includes an electric element, which electrically affects the other drive circuit.
 2. The drive unit according to claim 1, wherein one of the drive circuits has an output terminal, wherein the other drive circuit has an input terminal, and wherein the output terminal is connected to the input terminal.
 3. The drive unit according to claim 1, wherein the electric element forms a smoothing circuit for stabilizing the applied voltage from the power source.
 4. The drive unit according to claim 3, wherein the drive circuits share the smoothing circuit.
 5. The drive unit according to claim 1, wherein the electric element forms a filter circuit for filtering noise from the power source.
 6. The drive unit according to claim 5, wherein the drive circuits share the filter circuit.
 7. The drive unit according to claim 1, wherein the power source is a direct-current power source, which has a high potential terminal and a low potential terminal, and the actuator drive circuit includes a switching element, which has a first terminal and a second terminal, wherein the electromagnetic actuator includes a coil, which has a first terminal and a second terminal, wherein the first terminal of the switching element is connected to the high potential terminal of the direct-current power source, and the first terminal of the coil is connected to the low potential terminal of the direct-current power source, and wherein the second terminal of the switching element is connected to the second terminal of the coil.
 8. The drive unit according to claim 7, wherein a shunt resistor is arranged between the low potential terminal of the direct-current power source and the first terminal of the coil, and wherein the shunt resistor is used for detecting the value of the current flowing through the coil.
 9. The drive unit according to claim 1, wherein the power source is a direct-current power source, which has a high potential terminal and a low potential terminal, and the actuator drive circuit includes a switching element, which has a first terminal and a second terminal, wherein the electromagnetic actuator includes a coil, which has a first terminal and a second terminal, wherein the first terminal of the switching element is connected to the low potential terminal of the direct-current power source, and the first terminal of the coil is connected to the high potential terminal of the direct-current power source, and wherein the second terminal of the switching element is connected to the second terminal of the coil.
 10. The drive unit according to claim 9, wherein the motor is an AC motor, and the motor drive circuit includes a plurality of phase inverter circuits, wherein each phase inverter circuit includes a high-side switching element, which has a first terminal and a second terminal, and a low-side switching element, which has a first terminal and a second terminal, wherein the first terminal of the high-side switching element is connected to the high potential terminal of the direct-current power source, and the first terminal of the low-side switching element is connected to the low potential terminal of the direct-current power source, wherein the second terminal of the high-side switching element and the second terminal of the low-side switching element are connected to the AC motor via a common AC output terminal, and wherein the low-side switching element and the switching element of the actuator drive circuit are driven by a common drive source.
 11. The drive unit according to claim 1, wherein the motor is a DC motor.
 12. The drive unit according to claim 11, wherein a power line extending from the motor drive circuit to the motor and a power line extending from the actuator drive circuit to the electromagnetic actuator are partially shared.
 13. The drive unit according to claim 1, wherein the compressor includes a control chamber and a control valve, wherein the control valve has the electromagnetic actuator, and the opening degree of the control valve is adjusted by the electromagnetic actuator to change the pressure in the control chamber, and wherein the displacement of the compressor is varied in accordance with the pressure in the control chamber.
 14. The drive unit according to claim 1, wherein the compressor is incorporated in an air-conditioner of a vehicle, and wherein the compressor is actuated by selectively using the engine of the vehicle and the motor.
 15. A drive unit of a compressor that is actuated by a motor to compress gas, wherein the compressor includes a control chamber and a control valve, wherein the control valve has an electromagnetic actuator, and the opening degree of the control valve is adjusted by the electromagnetic actuator to change the pressure in the control chamber, and wherein the displacement of the compressor is varied in accordance with the pressure in the control chamber, the drive unit comprising: a power source; a motor drive circuit located on a power supply path between the motor and the power source to drive the motor; an actuator drive circuit located on a power supply path between the electromagnetic actuator and the power source to drive the electromagnetic actuator; a command device, which sends a command signal to each of the drive circuits to control the drive circuits; and a single smoothing circuit for stabilizing the voltage applied to the motor drive circuit from the power source and the voltage applied to the actuator drive circuit from the power source.
 16. The drive unit according to claim 15, further comprising a single filter circuit, wherein the filter circuit filters noise from the power source to the motor drive circuit and noise from the power source to the actuator drive circuit.
 17. The drive unit according to claim 15, wherein the power source is a direct-current power source, which has a high potential terminal and a low potential terminal, and the actuator drive circuit includes a switching element, which has a first terminal and a second terminal, wherein the electromagnetic actuator includes a coil, which has a first terminal and a second terminal, wherein the first terminal of the switching element is connected to the high potential terminal of the direct-current power source, and the first terminal of the coil is connected to the low potential terminal of the direct-current power source, and wherein the second terminal of the switching element is connected to the second terminal of the coil.
 18. The drive unit according to claim 17, wherein a shunt resistor is arranged between the low potential terminal of the direct-current power source and the first terminal of the coil, and wherein the shunt resistor is used for detecting the value of the current flowing through the coil.
 19. The drive unit according to claim 15, wherein the power source is a direct-current power source, which has a high potential terminal and a low potential terminal, and the actuator drive circuit includes a switching element, which has a first terminal and a second terminal, wherein the electromagnetic actuator includes a coil, which has a first terminal and a second terminal, wherein the first terminal of the switching element is connected to the low potential terminal of the direct-current power source, and the first terminal of the coil is connected to the high potential terminal of the direct-current power source, and wherein the second terminal of the switching element is connected to the second terminal of the coil.
 20. The drive unit according to claim 19, wherein the motor is an AC motor, and the motor drive circuit includes a plurality of phase inverter circuits, wherein each phase inverter circuit includes a high-side switching element, which has a first terminal and a second terminal, and a low-side switching element, which has a first terminal and a second terminal, wherein the first terminal of the high-side switching element is connected to the high potential terminal of the direct-current power source, and the first terminal of the low-side switching element is connected to the low potential terminal of the direct-current power source, wherein the second terminal of the high-side switching element and the second terminal of the low-side switching element are connected to the AC motor via a common AC output terminal, and wherein the low-side switching element and the switching element of the actuator drive circuit are driven by a common drive source.
 21. The drive unit according to claim 15, wherein the motor is a DC motor, and wherein a power line extending from the motor drive circuit to the motor and a power line extending from the actuator drive circuit to the electromagnetic actuator are partially shared. 